This invention relates to a process for partially molding a pad on the surface of an automotive instrument panel and to a mold which can suitably be used for practicing the process.
Multilayered molded products, each consisting of an insert material, a surfacing material and a urethane foam sandwiched therebetween, are suitably employed for automotive interior equipment such as an instrument panel in order to achieve lightening, improvement of decorability and damping of the impact at collision. For example, the instrument panel 10 shown in FIG. 13 consists of a panel main body 12 serving as the base, a surfacing material 14 which is exposed on the interior side of a vehicle and a urethane foam 16 filled by foaming in the space defined between the panel main body 12 and the surfacing material 14, and the entire panel is allowed to function as a pad with the aid of the foam filler. As the panel main body 12, for example, rigid resins which can easily be subjected to compression molding or injection molding, such as thermoplastic resins including polyethylene, polypropylene, nylon, and acrylonitrile-styrene, incorporated with a glass filler can suitably be employed. Meanwhile, as the surfacing material 14, a thermoplastic resin sheet, a thermoplastic elastomer film, etc. can be employed.
As such instrument panel 10, there are (1) those entirely covered with the surfacing material 14 and (2) those partially provided with the pad at the necessary portions of the panel main body 12 as seen in relatively inexpensive cars. Namely, in the latter example, a pad consisting of the surfacing material 14 and urethane foamed onto the rear surface of the surfacing material 14 is designed to be applied to the necessary portions of the panel main body 12, and the main purpose is to meet the requirement of reducing the production cost. As a technique for partially applying the pad on the surface of the panel main body, it is conventionally practiced, as shown in FIGS. 11 and 12, to form beforehand a pad 18, consisting of a surfacing material 14 and a urethane foam 16, to be applied partially onto the panel main body 12, and then the pad 18 thus formed beforehand is fitted onto the necessary portions of the panel main body 12. The pad 18 has protrusions 18a to be inserted to the panel main body 12, and a bendable tongue 20 is embedded in each protrusion 18a and extended partly outward. The panel main body 12 has a setback 12a and grooves 12b. The setback 12a has a depth such that the surface of the pad 18 fitted on the panel main body 12 may coincide with the surface of the panel main body 12, whereas the grooves 12b allow insertion of the projections 18a of the pad 18 therein. As shown in FIG. 12, the pad 18 can partially be applied onto the panel main body 12 with the pad surface coinciding with the panel surface, by fitting the pad 18 in the setback 12a of the panel main body 12 and inserting the protrusions 18a in the corresponding grooves 12b. By bending the tongues 20 inserted to the through holes defined in the grooves 12b after the pad 18 formed beforehand is thus fitted onto the panel main body 12, the pad 18 is prevented from slipping off the panel main body 12.
The conventional method of partially fitting the pad 18 formed beforehand onto the panel main body 12 involves the following problems which must be solved. First of all, while the pad 18 is formed by foaming urethane onto the rear surface of the surfacing material 14 using a mold independent of the panel main body 12, the yield of the surfacing material 14 in the molding is extremely low, disadvantageously. Further, since the tongues 20 for preventing slipping off of the pad 18 from the panel main body 12 must be embedded in the pad 18, the cost of the parts and the number of step are increased, disadvantageously. In addition, not only a step of cutting the superfluous portions of the surfacing material 14 in the pad 18, but also another step of fitting the pad 18 onto the panel main body 12 become necessary. Moreover, it can be pointed out that, since the pad 18 formed beforehand is to be fitted onto the panel main body 12, nonuniformity occurs in the accuracy of fitting the pad 18 depending on the skill of the worker.
With a view to overcoming these problems, the inventors of the present invention previously proposed a process for partially molding a pad onto an instrument panel, as detailed below. The process comprises (1) molding preliminarily a surfacing material having a predetermined pad profile and also an edge portion, along the periphery thereof to stand toward the rear surface thereof; (2) separately molding preliminarily a panel main body having a predetermined shape and also a recess, formed on the front surface of the main body, which receives the edge portion; (3) setting the surfacing material and the panel main body on the cavity wall of a lower die and on the core of an upper die, respectively; and (4) filling the space defined between the panel main body and the surfacing material with urethane under foaming, followed by mold releasing. However, when such pad molding process is actually practiced, the following drawbacks can occasionally be pointed out. Namely, as shown in FIGS. 10(a) and 10(b), the edge portion 22 standing from the periphery of the surfacing material 14 toward the rear surface thereof sometimes fails to smoothly slip in the groove 24 defined in the panel main body 12 and falls outward, when the upper die is closed with respect to the lower die. In other words, since the surfacing material 14 itself has no rigidity, the panel main body 12 when descended together with the upper mold is brought into contact with the edge portion 22 to push and uncorrectably fell it outward as shown in FIG. 10(b). The thus obtained instrument panel is defective and cannot be used. Therefore, a means for preventing the edge portion from falling outward becomes necessary.
The process for partially molding a pad according to one aspect of the invention is proposed with a view to overcoming the problems inherent in the process described above, and it is an objective of the invention to provide a means which requires no molding of the pad, consisting of a surfacing material and urethane independent of the panel main body but can achieve partial molding of the pad onto the panel main body through one step to improve yield of the surfacing material, and which can omit the steps of cutting the surfacing material and the tongues for preventing slipping off of the pad, so as to eliminate the steps of incorporating the pad into the panel main body, giving excellent working accuracy. Meanwhile, in a pad molding mold according to another aspect of the invention, there is provided a means which can effectively prevent the edge portion standing from the periphery of the surfacing material toward the rear surface thereof from falling outward.